1. Field of the Invention
This invention relates generally to ion implantation processes in the manufacture of semiconductor integrated circuits. More particularly, this invention relates to a method of controlling the dose and energy of the ion implantation in the manufacturing process. Even more particularly, this invention relates to a method to precisely determine the dose and energy of a particular ion implant in the manufacturing process.
2. Discussion of the Related Art
In the typical semiconductor manufacturing facility, many simulation and analysis tools have been implemented to assist the process integration and device development efforts. These simulation and analysis tools, however, are typically employed to provide an indication of general trends. The latent potential of reducing the number of silicon runs and speeding up the process optimization cycle has not been fully achieved. One of the primary reasons the process optimization cycle has not been achieved is that the accuracy of the data obtained cannot be established to the degree necessary to determine the dependability of the simulations systems. The accuracy of the data obtained can only be achieved by a complete and detailed engineering calibration of the simulation system. This calibration, however, demands extensive engineering resources and data from multiple silicon production runs which, in turn, is usually only available at the latter stages of the process development or early production cycles.
In addition, process optimization for a technology that has completed qualification and is ramping-up production could receive great benefit from the extensive embedded device physics contained in advanced complex simulation tools. Despite this extensive knowledge base, statistical data analyzing tools dominate, to the near exclusion of device simulation tools, as the tools employed in the decision making process in modern semiconductor manufacturing facilities. The main reasons for this are as follows:
1. The manufacturing data is fundamentally statistical. It is usually impossible to control, much less measure exact values for many process parameters. Moreover, if the simulation, or even the actual silicon itself, yields only a single data point without accompanying distribution information, that result is usually insufficient to justify any qualified decision.
2. Process monitoring and optimization is an ongoing and reiterative sequence of fine-tuning that is dependent upon barely measurable differences which are affected by statistical fluctuation in process and complicated interactions between various process parameters. Therefore, a truly useful tool that an engineer can trust must provide a high order of data accuracy.
3. Vast amounts of process variables, in-line measurements and electrical data are continually collected in the manufacturing facility (fab). Current existing simulation tools, however, cannot effectively utilize this data.
Problematically, statistical analysis alone, without integration of the existing knowledge of device physics and simulation skills, is neither flexible nor powerful enough to handle engineering changes in the process without sufficient accurate actual data from the silicon itself.
Current semiconductor processing for advanced semiconductor processing technologies use a multiplicity of ion implanted layers in the manufacture of the semiconductor integrated circuits. The typical ion implant process is to implant dopant ions into a layer of semiconductor material to adjust a parameter of the semiconductor device. For many of these layers, precise control of the dose (dopant ions/cm.sup.2) and the implantation energy (KeV) is critical for proper operation of the semiconductor integrated circuit. Current methods of measuring does and energy are not accurate enough to observe differences in the dose or implantation energy that will "kill" (make the device fail) the device. The trend towards smaller and smaller devices and more and more circuits on a device have exacerbated this problem.
One approach to solve this problem would be to have an array of ion implant monitor structures incorporated directly on the wafer such that at each implant layer mask the structure that corresponds to that layer would be open and receive the implant, while all the other ion implant monitor structures in the array are covered. After the processing of the wafer is completed, these structures would be made into metal gate devices that can be CV (capacitance/voltage) measured for implant profile, dose and energy. The problems with this method include the variability of the process, thermal budget and background concentration. These problems render this method untenable or at least inaccurate.
Therefore, what is needed is an accurate method to provide precise measurements of intrinsic process parametrics so that an accurate dopant dose and energy implant level can be determined for each and all ion implantation process steps.